The present invention relates to a radiation generator used as a source for generating a synchrotron radiation beam.
Synchrotron radiation beam (hereafter referred to as "radiation beam") technology has recently attracted attention, especially its possible application to the lithograph and semiconductor-processing techniques. However, the radiation beam is produced in a high vacuum atmosphere of at least approx 10.sup.-10 Torr. Therefore, to apply the beam to various techniques, it is necessary to extract a radiation beam without lowering the vacuum level of the atmosphere. This type of generator is disclosed, for example, in the Japanese Patent Laid-Open, No. 156200/1990 which corresponds to U.S. Pat. No. 4,996,700. This radiation generator has a multistage axial-flow turbine arrangement in which a plurality of stator blades and a plurality of rotor blades are alternately arranged in the axial direction. These are interposed in a beam duct disposed for extracting a radiation beam from an electron storing ring so that the radiation beam passes through the multistage axial-flow arrangement when the beam aperture 164, a "hole" formed in the blade 163 of the stator 161 shown in FIG. 9, and the gap 166 between blades 165 of the rotor 162 shown in FIG. 10 are aligned. Therefore, it is possible to extract a radiation beam regardless of its wavelength and go provide an easy-to-use radiation generator with a short beam duct.
However, this radiation generator has a problem, It is impossible to efficiently extract a radiation beam from a high vacuum atmosphere because the beam aperture 164 in the blades 163 of the stator 161 is always open and thereby, the compression ratio of the multistage axial-flow arrangement is decreased because residual gas flows backward through the beam aperature 164. Thus, it is difficult to keep the electron storing ring side at a high vacuum level.